There is a need for high-speed cost effective optical transmitters which can operate as parallel optical communications data links. The preferred method of transmission for voice and data information across a network is by optical fiber due to bandwidth capacity and lower signal attenuation as compared to traditional copper networks. The light emitting and light receiving devices are referred to as optoelectronic devices and they are generally coupled at a first end to one or more fiber cables. The optical fibers provide the path for photons created by an optoelectronic device, such as a semiconductor LED or laser. An opposing end of the fiber cable is connected to a light-receiving device such as a photo detector.
The primary function of the optical transmitter is to translate electrical signals into optical signals. The optical transmitter interfaces with an electric interface circuit for driving the light transmitting device. A parallel optoelectronic module or package may include both receiver and transmitter functions.
The coupling of an optoelectronic device with an array of optical fibers at a first end and an interconnecting substrate at the opposing end is a difficult task for every time a coupling is made the quality of the signal transmission is affected. In a typical coupling, an optical connector is employed for efficiently managing the transfer of photons from the light-emitting device to the fiber optic cable. The optical connector must be aligned and connected with the optoelectronic device. The coupling of such systems generally require precise alignment for signal quality decreases with increased distances from an optical port to an optical connector unless the photons are properly directed into the fiber cable. The alignment techniques necessary to achieve such precise alignment are typically performed manually which is both time consuming and expensive.
Optical connections are only half the battle of effective coupling. Connection of the optoelectronic device with the electronic interface substrate of the package is complicated due to geometric constraints. The optoelectronic transmitter commonly used in fiber optic networks is the vertical cavity surface emitting laser (VCSEL). Unfortunately, the VCSEL emits light in a generally perpendicular direction to the plane of the fibers and substrate therefore making stacking of such components difficult. To solve the packaging problem the VCSEL is either mounted parallel to the substrate and the output photons directed 90° through mirrors or the VCSEL is mounted perpendicular to the substrate and the electrical interface connectors bent 90°. The optical bending solution is less than optimal due to the difficult optical design and alignment required. Conversely, the bending of electrical conductors is well known in the art through implementation of flexible circuits. Therefore, flexible electrical circuits capable of achieving the necessary 90° bend are the generally accepted solution.
In order to reduce electrical parasitics, short electronic interconnects are needed between the optoelectronic device and the electronic interface circuitry. The problem alignment and bending of the flexible circuit are exacerbated as data rates of the optoelectronic devices increase, closer connections must be established in order to maintain electrical performance levels. The placement and bending of the flexible circuit on the substrate is typically performed manually by a skilled technician just prior tot application of an adhesive. Unfortunately, the existing techniques employed in connection with this process are time consuming, expensive and prone to failure due to misalignment. If the placement of the flexible circuit fails to align with the substrate connectors, the entire component may need to be scrapped. While manual bending and aligning techniques exist for mounting an optoelectronic device to the substrate, it would be desirable to improve the efficiency and reduce the cost of the coupling.